Donor‐Derived Cell‐Free DNA in Stable Pediatric Kidney Transplant Recipients: Influence of Donor Obesity and Recipient Size

BACKGROUND: Donor-derived cell-free DNA (dd-cfDNA) is increasingly used as a noninvasive marker of kidney allograft injury, but adult-derived cutoffs may not be applicable to pediatric recipients, particularly in the setting of donor-recipient size mismatch. We evaluated dd-cfDNA levels in stable pediatric kidney transplant (KT) recipients and assessed variation by recipient weight and donor body mass index (BMI). METHODS: Retrospective data were collected from seven U.S. pediatric KT centers. Clinically stable recipients < 18 years of age (no de novo donor specific antibody, biopsy-proven rejection or BK viremia/nephropathy), with ≥ 2 dd-cfDNA measurements per year were included. Recipients were stratified by weight at dd-cfDNA collection (< 20 kg, 20-50 kg, > 50 kg). Donor BMI was categorized as underweight (≤ 18.5), normal (18.6-24.9), overweight (25-29.9), or obese (≥ 30). Comparisons were performed using linear mixed-effects models. RESULTS: Among 178 recipients, mean dd-cfDNA did not differ by recipient weight (< 20 kg: 0.51 ± 0.44; 20-50 kg: 0.65 ± 1.28; > 50 kg: 0.49 ± 0.70). Median dd-cfDNA was similar across donor BMI categories. However, among obese donors, recipients < 20 kg had 1.3-fold higher dd-cfDNA (p = 0.044). Donor-recipient body surface area mismatch > 1.5 was associated with 1.083-fold higher dd-cfDNA up to 5 years post-transplant (p = 0.016). CONCLUSIONS: or in the setting of a donor-recipient BSA mismatch > 1.5 were associated with higher dd-cfDNA levels.